remove read lock when fetching specific attribute (#5413)
remove read lock when fetching specific attribute (#5413)

## What is the goal of this PR?
Following the @marco-scoppetta 's investigation on Janus transaction isolation levels, we realised that we do not further require read locks when getting a specific attribute. Consquently we remove them.

## What are the changes implemented in this PR?
Remove read lock when performing a PUT attribute operation.

lolski/grakn,graknlabs/grakn,graknlabs/grakn,lolski/grakn,graknlabs/grakn,lolski/grakn,graknlabs/grakn,lolski/grakn